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This patch improves the performance of the planning phase of a query querying HBase tables. It removes an unnecessary second call to compute stats and adds a new version for estimating the row count in a table. This patch adds an incremental version to estimate the number of rows for a set of regions. This incremental version will start querying up to five regions to calculate the average row size and use this value to estimate the row count based on the size of the regions on disk. Only if the standard deviation from the average is larger than 15% query an additional region, it will query additional regions to calculate an average with more confidence. If the data is balanced it will not be necessary to retrieve data from all regions but only from a subset. In the worst case, all regions are queried. Change-Id: Idcb3bea81b11cb08da6d9329ba66c86aca23e170 Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5258 Tested-by: jenkins Reviewed-by: Martin Grund <mgrund@cloudera.com>